Update composer.json

upgrade phpstan to ^2.1

Author: vredeling

composer.json

@@ -28,7 +28,7 @@
   },
   "require-dev": {
     "friendsofphp/php-cs-fixer": "^3.4",
-    "phpstan/phpstan": "^1.5",
+    "phpstan/phpstan": "^2.1",
     "phpunit/phpunit": "^9"
   },
   "autoload": {